ROOF DRAINS


The immediate draining of water on the exposed surfaces of a building such as roofs, balconies, etc. is important to protect the structure of the building from corrosion and moisture. Gravity-type or vacuum-type systems can be used for drainage. Siphonic systems (Bernoulli effect) are used to drain large surfaces and especially impassable areas where dirt is limited in space. In case of blockages, the standard EN 1253 provides for the additional use of gravity type safety drains, in case of overflow.

The most common and safest way of drainage, especially in areas such as Greece, with extensive drought and extreme rainfall that create blockages from the winds in the systems, is the use of gravity systems. An important factor in choosing systems is:

1) the cooperation and consistency of the drain with the bituminous waterproofing membranes or the wet insulation 2) the correct choice of grate both for the avoidance of blockages and for the correct choice of loading class in case of accessible space.

The degree of filling in the pipes according to EN 12056 should not exceed 0.7 as proper ventilation is required for safe and secure drainage. The flow rate for each area is calculated with the following formula:

  • Q=r (height of rain L/s* ha) * C * A (area m2) /10.00


The runoff rate according to the German DIN 1986-100 is:

Τύπος επιφάνειας Συντελεστής απορροής (C)
Membrane, Cement, Asphalt, tile 1.0
Gravel, Green roof with a thickness of less than 10cm 0.5
Green roof with a thickness greater than 10cm 0.3
The calculated flow can be used to select the number of drains as well as their correct cross section.

For the products it supplies, Enflow, in collaboration with the companies it represents, can dimension the siphonic system based on the requirements of each project.